Knowledge of the mechanisms employed by animal cells in regulating the production of cytoplasmic messenger RNA (mRNA) is fundamental for an understanding of development and how the factors which control normal cellular growth are altered in the cancerous state. Data pertaining to the structure of the mRNA as well as its synthesis and transport indicate that in cultured animal cells some, and possibly most, mRNAs are derived from larger nuclear precursors (HnRNA). HnRNA contains regions which corresponds to mRNA sequence as well as several, common, putative regulatory regions (referred to as Oligo(U), Oligo(A), double stranded RNA, and rapidly hybridizing RNA) which are destroyed in the nucleus and not present in mRNA. This suggests that the pathway producing different mRNAs may contain several common reactions. This application proposes additional investigation of HeLa cell HnRNA regarding the structure and location of these "non mRNA" sequences and their possible involvement, either directly (as sites for nucleases) or in association with other RNA or protein molecules, in the processing of mRNA sequences. An understanding of the processing reactions may reveal whether they are modified to alter the supply of mRNA according to growth or developmental requirements or changed when cells are transformed by DNA tumor viruses. Transformation is known to involve the integration of viral DNA into the host genome and the production of viral RNA. It is not known how the presence of viral mRNA(s) causes a loss of control of cellular growth, however, the production of cytoplasmic mRNA seems to be altered. Cells transformed by DNA tumor viruses appear to contain some mRNA sequences not found in their untransformed counterparts. Also, while the production of mRNA is inhibited in normal fibroblasts by aminopuromycin, transformed fibroblasts are not affected by the drug. Investigation of the structure of viral specific HnRNA in transformed cells may reveal the nature of the cellular DNA sequences adjacent to the integrated viral DNA and whether the transcribed viral RNA sequences are processed similarly to cellular mRNA.